1. Field of the Invention
The present invention relates generally to electrochemical power sources. More particularly, the present invention relates to a fuel particle feeding apparatus that provides zinc fuel particles into a rechargeable zinc/air power source.
2. Description of the Related Art
There has been a renewed interest in zinc/air batteries for electric vehicle propulsion because of the unique combination of high-energy density and low hardware cost. If the zinc/air battery can be made mechanically rechargeable by a simple and rapid technique, the battery can provide an electric vehicle with unlimited range extension, without resorting to slow electrical recharge, battery exchange, component replacement, or combustion engine hybrids. The option of mechanical recharge or refueling is important in fleet electric vehicles such as shuttle buses and delivery vans and other industrial or enclosure-operated vehicles, which often must operate over eight hours each day to effectively return the high cost of the vehicle. Using battery exchange methodologies essentially doubles the battery investment, while range extension using combustion engines defeats the primary purpose of emission-less power sources.
It is possible to divide mechanically-recharged battery concepts into two groups: (1) reconstructible cell batteries, and (2) refuelable cell batteries. Reconstructible cell batteries are characterized by the physical removal and refurbishing of battery components such as anode plates or cassettes, or even unit cells. Reconstructible cell batteries have been developed by Electric Fuel, Ltd. of Israel, and have demonstrated ranges of over 260 miles in delivery vans in Germany and Italy. Anode cassettes are moved (along with unconsumed zinc and zinc-oxide by-products) by robotics and reconstructed at an industrial plant. Advantages of simplicity must be balanced against the cost of industrial infrastructure. Moreover, anode consumption is incomplete and the cells are incapable of partial recharge.
Refuelable batteries use an electrochemical fuel, which is pumped into the battery in a manner that is similar to refueling an automobile. For this reason, they are often referred to as fuel cells or regenerative fuel cells. All cell hardware remains on the vehicle and is undisturbed by the refueling operation. The purpose of seeking a refueling technology is to eliminate the cumbersome battery replacement operation and requirements for centralized industrial infrastructure to support vehicle operation. Unlike cell reconstruction, the recovery of zinc from battery reaction products as a fuel can be accomplished using small-scale electrolysis equipment that is owned and operated by the fleet and conveniently located at the fleet's home base. Examples of refuelable batteries are the CGE zinc/air slurry battery and the concepts proposed by Evans or Alcazar or Cooper.
Prior art attempts to develop a rapidly refuelable zinc/air power source have met with limited success. One of the most important factors limiting the development of zinc/air fuel cells is the need for a convenient, rapid method for completely refueling the fuel cell.
Most of the prior art relates to methods of refueling a single cell and is thus not concerned with the rapid and complete refueling of a large number of cells in a stack. Some of the related prior art includes the following U.S. Patents Cooper, Pat. No. 5,434,020; Nunnally, Pat. No. 5,869,200; Siu, et al. Pat. No. 5,849,427; Siu, et al. Pat. No. 5,441,820; Evans, et al. Pat. No. 5,006,424; and Leparulo, et al. Pat. No. 3,847,671, all of which are incorporated herein by reference.
Cooper discloses an electrochemical cell with a tapered cell cavity for gravity feeding of fuel particles. Included in his disclosure is means for refilling fuel particle storage hoppers by hydraulic means. However, Cooper does not describe a practical method or apparatus for carrying out a hydraulic refueling operation. Additionally, the typical prior art hopper and feeding channel geometry shown in Pat. No. 5,434,020 and publications, (Society of Automotive Engineers Publication No. 951948 and Science & Technology Review, Oct. 1995 p. 8 published by Lawrence Livermore National Laboratory) uses a rapid electrolyte flow through the feed tubes and perpendicular to the plane of the fuel cell hoppers with a return path and no means for high speed electrolyte flow down into and parallel to the plane of the fuel storage hoppers. One drawback to this method is that it does not completely fill the storage hoppers because the particles simply fall into one end of the hoppers as they fall out of the rapidly flowing feed tube above and "mound" in the hoppers. The fragility of the separators between the fuel cell cavities in Cooper also teaches against an electrolyte flow into and parallel to the plane of the fuel cell hoppers. See U.S. Pat. No. 5,434,020, Col. 2, 11. 61-65.
Nunnally, Pat. No. 5,869,200 discloses a magnetic slurry fueled battery system with a magnetic field used to hold microparticle spheres to the battery cell electrode plates. One disadvantage is the complexity of the disclosed system. The complexity results in a higher cost system, and a higher potential for failure within such a complex system, when compared to other prior art technologies or the present invention. Another disadvantage is the need to use fuel particles containing ferromagnetic or permanently magnetic cores. This greatly increases the cost of the fuel. In any event, Nunnally does not disclose a method for ensuring rapid and complete refueling of cells or fuel storage hoppers.
Siu et al. Pat. No. 5,849,427 discloses a hydraulically refueled battery. A major disadvantage is the requirement for a shut-off valve on each cell to terminate refueling of each cell. For an electric vehicle, this would require hundreds of small valves. Therefore, higher costs are required, a large storage area for installation is required, and the real possibility of system failure exists because of the complexity of design.
Siu et al. Pat. No. 5,441,820 discloses an electrically recharged battery employing a spouted particle bed. A spouted bed as defined in this invention, is one where recirculation from a pump causes an upward flow in the electrolyte in a "draft tube". The purpose of the upward flow is to entrain particles and carry them to the top of the particle bed, plus keeping the bed in constant motion. Therefore, the metal particles are kept from agglomerating during recharge. No means for hydraulically refueling the cell is described.
Evans, et al. Pat. No. 5,006,424 discloses a battery using gravity to feed electrolyte and particles with a key feature being creating convective forces to recycle the electrolyte based on density. No method or apparatus for refueling this battery is described.
Leparulo et al. Pat. No. 3,847,671 discloses a hydraulically refuelable battery system. This device is so constructed that both solid and liquid content must be routinely drained from each cell after discharge, and prior to refueling. Some disadvantages to this design include the use of separate hydraulic hardware (valves, etc.) for each cell to provide a complex and large system. Therefore, a large storage area is required in addition to a relatively higher cost over some prior art systems.
In summary, despite many attempts, the known prior art has still not solved the problems associated with delivering metal particles to metal-anode-based refuelable cell stacks. These problems include slow refueling cycle times, mounding of particles in the cell hoppers, lack of uniform distribution of particles in the cell hoppers, clogging of metal fuel particles, excessive hardware complexity, uneven fill profiles, piling up of fuel particles, and overall slow or otherwise inefficient fuel particle feeding operations. Therefore, it is clear that a need exists for an improved fuel particle feeding mechanism. The present novel invention of a particle feeding mechanism, and the process of making and operating it, does provide numerous novel features that solve these problems and eliminates these disadvantages.